Method and apparatus for converting electric power



April 18, 1933. 1.. A. HAZELTINE 1,904,455

METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER Filed July 5, 1923 15 Sheets-Sheet 1 IN VENTOR LOUIS A. HAZELTINE ATTORNEY April 18, 1933- L. A. HAZELTINE 1,904,455

METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER Filed July 5, 1923 15 Sheets-Sheet 2 Fig. 5a

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METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER Filed July 5, 1923 15 Sheets-Sheet 3 FiglO LOUIS AHAZELTIN E INVENTOR ATTORNEY April 18, 1933. A. HAZELTINE 1,904,455

METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER Filed July 5, 1923 15 Sheets-Sheet 4 HQ 4 3 m w ujA IN VENTOR LOU/S A. HAZELTINE Valve Voltages Valve Currents ATTORNEY April 1933- L. A. HAZELTINE METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER Filed July 5, 1923 15 Sheets-Sheet 5 LOUIS A HAZELTINE INVENTOR v- Wm W /O ATTORNEY April 18, 1933. A. HAZELTINE 1,904,455

METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER Filed July 5, 1923 15 Sheets-Sheet 6 LOUIS A. HAZELTINE INVENTOR BY a l h v f/WM"? ATTORNEY April 18, 1933. L, A L NE 1,904,455

METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER Filed July 5, 1923 15 Sheets-Sheet 7 Fig.3@

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Cu Fren ts Voltages A TTORNE Y April 13, 1933- L. A. HAZELTINE 1,904,455

METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER Filed July 5, 1923 l5 Sheets-Sheet 10 Currents Voltages x), ,.4 LOUIS A -HAZELTINE i 11v VENTOR a x B? AD I -WM M W ATTORNEY April 18, 1933- 1.. A. HAZELTINE 1,904,455

METHOD'AND APPARATUS FOR CONVERTING ELECTRIC POWER Filed July 5, 1923 15 Sheets-Sheet 11 Fig. 49

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LOUIS A. HAZEL FINE INVENTOR ATTORNEY April 18, 1933. L. A. HAZELTINE 1,904,455

METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER v Filed July 5, 1923 15 Sheets-Sheet l2 LOUIS HAZELTINE INVENTOR By M M /o WM ATTORNEY April 18, 1 L. A. HAZELTINE METHOD AND APPARATUS FOR CONVERTING'ELECTRIC POWER l5 sheets sheet 13 Filed July 5, 1923 Fig. 56

[T TTT LOUIS A. HAZELTINE IN V EN TOR A TTORNE Y April 18, 1933- L. A. HAZELTINE I 1,904,455

METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER Filed July 5, 1923 15 Sheets-Sheet 14 C; Fig.57a

LOUIS AHAZELTINE INVENTOR W BY /0@ A TTORNEY April 18, 1933- L. A. HAZELTINE 1,904,455

METHOD AND APPARATUS FOR CONVERTING ELECTRIC POWER 0\ O A I 2% a! W59 LOUIS A HAZELTINE INVENTOR ATTORNEY Patented Apr. 18, 1933 UNITED STATES PATENT OFFICE I LOUIS A. HAZELTINE, OF HOBOKEN, NEW JERSEY, ASBIGNOB '10 GENERAL mo COMPANY, A CORPORATION OF NEW YORK METHOD AND APPARATUS FOR CONVERJIITG ELECTRIC POWER Application fil ed July 5,

This invention relates to a method and apparatus for improving the efiicrency of electric valve converters with a mmlmum production of current and voltage harmonics. It consists of improvements and extensions of the methods disclosed in United States Letters Patent No. 1,835,156, granted December 18 1931.

\ iBroadly speaking an electrlc valve 1s a device whose resistance can be controlled for the purpose of varying the current passlng through it. An electric valve converter consists of one or more electric valves and associated circuits which convert one form of electric energy into another. Exam les of electric valve converters are: (1) T e mechanical commutator, which converts alternating current into direct current, direct current into alternating current, alternating current of one frequency into alternating current of another frequency, or alternating current from one phase of a polyphase system to another in such manner as to supply or absorb reactive power; (2) the arc rect1- her, which converts alternating current into direct current; (3) the arc oscillator, WhlCh converts direct current into alternating current; (4) the vacuum-tube rectifier; (5) the vacuum-tube oscillator; (6 the vacuum-tube amplifier, which converts irect current into alternating current of electrlcally controlled wave form; (7) the microphone, wh1ch converts direct current into alternating current of sound-controlled wave form; an (8) the crystal rectifier, which usually converts modulated highfrequency alternating current into modulated direct current.

The resistance of an electric valve may vary graduall from one value to another, as

in the ampli er and in the microphone, or

abruptl from a very low value to a very high va ue, as conspicuously in the mechanical commutator. With gradual variation in resistance, there is necessarily a relatively large power loss in the valve itself, and hi h efiiciency of conversion is-impossible. n the other hand, with an abrupt change in resistance, the voltage drop in the valve will be small when the resistance is at its low value, and the current will be small (usually 1923. Serial No. 649,588.

zero) when the resistance is at its high value (usually infinite) ;'the ower loss is thus low at all times and the e ciency of conversion is therefore high.

We may speak of an abruptly operated valve as being closed when its resistance is relatively low and as being 0 en when its resistance is relatively high. lhroughout the interval when the valve is closed, the desired voltages of the input and output circuits will not usually be equal; and for high efiiciency the difference between these voltages must be absorbed in a highly reactive Impedance. Throughout the interval when the valve is open, the desired currents of the input and output circuits will also not usually be equal; and their difference must be absorbed in a highly reactive admittance. If these means are not provided for absorbing voltage and current differences, then either a substantial 70 power loss will exist in the valve or else the wave forms of input or output current and voltage will be distorted from the desired forms. In my patent referred to, are shown means for absorbing voltage differences (as the impedance coil 25 Fig. 8) and means or absorbing current dlfierences (as the condenser 31, Fig. 8),. the specific arrangement being an oscillator employing electrostatically controlled vacuum-tube valves,. or triodes.

Certain conversions of electric power are attained by stationary apparatus involving only the phenomena of electromagnetic inductance and electrostatic capacity. These are: (1) The step ing up or down of alternatin voltage; 2) the chan 'ng of one polyp ase system to another; (3 the changmg of a constant-voltage alternating current system to a constant-current alternatingcurrent system, or vice versa; and (4) the supply or absorption of reactive power. All of these conversions occur without change in frequency and without change from polyphase to single-phase or vice versa.

Other conversions of electric energy are attained by electric valves. 'These are (1) the conversion of alternatin current into direct current or vice versa; 52.) the convers'ion of alternating current of one frequency 100 into alternating current of another frequency; (3) the conversion of polyphase alt ernating current into single-phase alternating current of the same frequency, particularly a low frequency, or vice versa; (4) the stepping up or down of direct voltage; (5) the changing of a constant-voltage direct-current system to a constant-current direct-current system, or vice versa; (6) the conversion of direct current into alternating current of controlled wave form (e. g., voice current in telephony) (7) the supply or absorption of polyphase reactive power without corresponding energy storage (as in condensers or inductive coils respectively) (8) the change or reversal in the effective reactance of a coil or a condenser. These conversions may be combined in various ways. Only the first two of these conversions form the specific subject matter of the present invention; the remainder will be described specifically in applications for Letters Patcut about to be filed.

As in my patent referred to above, which shows methods for converting direct-current power into alternating-current power, in all valve converters in circuits where the input and output voltages differ in wave form dur-- ing the cyclic intervals when the valves are closed, a series impedance is required in one of the circuits to absorb this voltage difference; and Where the input and output currents differ in wave form during the cyclic interval when the valves are open, 'a shunt admittance is required in the other of the circuits to absorb this current difference. The conversions considered in this patent application are all of this class, the alternating currents and voltages being sinusoidal and the direct currents and voltages being constant from instant to instant. These conversions have been applied in the past in certain fields, by the use of commutators, which are mechanically controlled valves, but the problem of wave form has either not entered or has not been completely solved. Furthermore the ordinary commutator has certain limitations, such as permitting only moderately low frequency, producing undesirable temporary short circuits between bars when these are spanned by a brush, and requiring operation in regular order and usually at equal time intervals. While this invention is applicable in some of its details to mechanically operated valves, its main purpose is to provide stationary valves and appropriate circuits, and specifically to provide a highly eflicient form of electrostatically controlled valve converter of the thermionic type.

A specific application of the valve conversion of this invention is the operation of electric railways. The most desirable form of power transmission over considerable distances is by the use of three-phase alternating current, since alternating current is most easily transformed in voltage. The most desirable form of power for delivery to electric locomotives and cars is high-voltage direct-current, since this requires only a single contact conductor and avoids the interference with communication lines that is experienced with single-phase alternating current. The most desirable type of motor would be the polyphase squirrel-cage induction motor supplied with currents of adjustable frequency, since this motor has no sliding contacts and is most robust in construction, but requires variable frequency for efficient speed control. 'These conflicting demands for the form of power can be reconciled by the use of valve converters, first converting three-phase alternating-current into high-voltage direct current at sub-stations and then converting the direct current into variable-frequency polyphase current on the locomotive or cars.

The direct conversion between direct current and low-frequency alternating current requires a very large number of valves unless the voltagcabsorbing and current-absorbing coils and condensers are made large; moreover, the residual harmonics with a small number of valves would have a frequency within the audible range and would therefore be likely to cause interference with telephone circuits. Further, the form of valve which forms part of this invention is most suited to moderately high control frequency. For these reasons the conversions at the substations and on the electric locomotive or car are each made in two steps; at the sub-station the conversion is from low frequency to moderately high frequency and then from this high frequency to direct current; on the electric locomotive or car the conversionis the reverse. from direct current to moderately high frequency and from this high frequency to low variable frequency. These two conversions being the same in form, but reverse in sense, only the latter will be described in detail. On the electric locomotive all of the main circuit connections are permanent, thus avoiding heavy contacts and rheostat losses. The speed control is effected wholly by adjustments in the control electrode circuits, these electrodes being controlled ultimately through a commutator.

The valve forming a part of this invention is of the magnetically guided, electrostatir cally controlled, thermionic type, in which (when the valve is closed) the electrons are accelerated from the cathode by a highly positive control electrode (in the form of a grid) and are constrained to move along lines of magnetic flux so that they pass between the rods of the grid without reaching them, and then, being attracted by the control electrode, retard to a low velocity before reaching the anode. (Usually the main electrodes are each alternately anode and cathode and are therefore both maintained electron-emissive, as by heating.) In this way the voltage drop in the valve circuit is kept very low, and the grid current practically negligible, although the grid potential may be very high. Another feature of this valve is the enclosing of the electrodes within concentric metal shells which reflect back to the electrodes the heat developed by the losses, the design being such that this heat maintains the emission from the main electrodes.

It should be understood that the accommnying drawings, while they illustrate emhodiinents of the invention, show only a few of the many possible arrangements which achieve the same ends, but they illustrate the preferred forms for the more usual apphcations and the principles according to which other forms may readily be developed.

Referring to these drawings,

Fig. 1a is the same circuit as Fig. 8 of my patent referred to above and illustrates a valve oscillator for converting direct-current power into single-phase alternating-current power particularly of high frequency. Fig. 1b is the same as Fig. 1b of the same patent, and shows the wave forms of current and voltage of Fig. M.

Fig. 2 is the same circuit as Fig. 9 of the same patent and illustrates a valve oscillator for converting direct-current power into polyphase alternating-current power.

Fig. 3a also shows an oscillator for converting direct-current power into polyphase alternating-current power. but employs only three valves. Fig. 3b shows the wave forms of current and voltage of Fig. 3a.

Fig. 4a represents a valve converter like that of Fig. 2, but for power conversion in either direction. Fig. 4b shows the current and voltage waves of Fig. 4a.

Fig. 5a is a modification of Fig. 4a to give operation similar to that of Fig. 3a. Fig. 5b shows the current and voltage waves of Fig. 5a.

Fig. 6a is a further modification of Fig. 4a. Fig. 6b shows the current and voltage waves of Fig. 6a.

Fig. 7 shows the Waves of direct current and alternating voltage for Figs. 4a,, 5a and 6a.

Figs. 816 each shows a generalized directcurrent-three-phase valve converter with various arrangements of the valves with respect to the direct-current circuit and with respect to the arrangement of the impedance coils.

Fig. 17a illustrates a direct-current-polyphase valve converter of the circuit-opening type, in contradistinction to the previous converters which are of the circuit-closing type.

Fig. 176 shows the wave forms of voltage and current of Fig. 17a.

Fig. 18a shows a modification of the circuit of Fig. 17a, in which the interval of opening of each valve is. changed. Fi 187) shows the wave forms of voltage an current of Fig. 180.

Fig. 19a shows another modification of Fig. 17a. Fig. 191) shows the wave forms of voltage and current of Fig. 19a.

Fg. 20 shows the waves of direct voltage and alternating current for Figs. 17a, 18a and 19a. 7

Figs. 21, 22 and 23 show modifications of the circuits of Figs. 17a, 18a and 19a respectively.

Figs. 24, 25 and 26 also show modifications of the circuits of Figs. 17a, 18a and 19a respectively.

Figs. 2735 each shows a generalized circuit-opening direct-cilrrent-polyphase valve converter with various arrangements of the valves with respect to the direct-current circuit and with respect to the arrangement of the tertiary circuits. I

Figs. 3643 show polyphase-polyphase circuit-closing valve converters with various arrangements of the valves with respect to the input and output circu ts.

Figs. 44 and 45 show the wave forms of current and voltage respectively, for Figs.

36-43, when the impedance side of the converter has the lower frequency.

Figs. 46 and 47 show the wave forms of current and voltage respectively, for Figs. 36-43, when the impedance side of the converter has the higher frequency.

Figs. 48-53 show polyphase-polyphase circuit-opening valve converters with various arrangements of the valves w th respect to the input and output circuits.

Fig. 54 shows the main circuits of a preferred arrangement for converting directcurrent power in two steps into variable-frequency polyphase power for operating squirrel-cage induction motors on an electriclocomotive.

Fig. 55 shows an alternat ve to Fig. 54.

Fig. 56 shows a modification of the directcurrent valve structure of Fig. 54 or 55 to suit it to operation at one-half the voltage.

Fig. 57a shows the control electrode circuits for the direct-current valve structure of the converter of Fig. 54. Fig. 57?) shows the control electrode circuits for the altern atingourrent valve structure of the converter of Fig. 54.

F g. 58a shows an elevation in section of the complete valve structure of Fig. 54. Fig. 58?) shows a plan in section corresponding to Fig. 580.

Fig. 59 is a detail in plan and elevation of the valve structure of Figs. 58a and 58b.

Referring to Fig. 1a, 1b and 2 represent elcctrostatically controlled valves each having a cathode in the form of a heated filament, an anode in the form of a plate, and a control electrode in the form of a gr d interposed between the cathode and the anode.

Under the'control of the grids, the anode circuits of the two valves open and close alternately and so permit the direct current ing current in secondary coil 11, which supplies a load to be connected at the right. If the direct-current generator is to have a constant current and a constant voltage from instant to instant and the alternating current load is to have a sinusoidal-current and a sinusoidal voltage from instant to instant, and the valves are to operate substantially as ideal valves Without absorption of current or voltage, it is necessary to provide the condenser C to absorb the difference between the rectangular interrupted direct current and the sinusoidal alternating current, and to provide the impedance coil L to absorb the difference between the constant direct voltage and the half-sinusoidal rectified alternating voltage. On account of the phase relations demanded by the connection of the control electrodes to the coils 21, 22 of the output transformer, the frequency will automatically adjust itself so that the condenser C is resonant w th the transformer primary coil 31, 32 and its load; a large capacity and a low primary self-inductance are desirable, as affording a high admittance to the harmonic currents to be absorbed. As high a value of self-inductance at L as is consistent with a low resistance is desirable, as affording a high impedance to harmonic voltages. The wave forms of the valve or anode current i the valve voltage or anode potential 6,, and the control electrode potential 6 as actually obtained. are shown in Fig. 1?).

Fig. 2 consists simply of three single-phase valve oscillators, like that of Fig. 1a coupled by connecting secondary coils 11, 13, 15, in delta to synchronize them and to provide a three-phase oscillator. A triple-frequency current flows in this delta and so relieves the condensers of such harmonics.

Fig. 3a is like Fig. 1a except that three valves are employed instead of two, and three separate transformers, each with a shunting-condenser, are employed in place of the single transformer with the middle tap. This arrangement gives a three-phase oscillator in place of the symmetrical singlephase oscillator of Fig. 1a. The three valves 1, 2 and 3, or anode circuits, are closed in succession, each for one-third of a cycle, thereby causing the constant current of generator G to be broken up into three rectangular current lobes in the three primary coils 31, 32 and 33. These currents induce threephase secondary current, in coils 11, 12 and 13, which are to be connected to a threephase' load at the right. Coils 21, 22 and 23 of the same transformer supply potentials of the proper phase to the three control electrodes. As in Fig. 1a, condensers C C, and C are required to absorb the differences between the rectangular interrupted direct currents and the sinusoidal currents demanded by the load. Also, as in Fi 1a, the im the di erence between the constant direct voltage and the rectified sinusoidal voltages of the transformer primary coils. (In both figures, the coil L may connect to some other point of the transformer primary coil than the neutral point, but it will then be called on to absorb some of the fundamental sinusoidal voltage in addition to the harmoniw.) Again, as in Fig. 1a, the control electrode circuit requires an impedance coil L for the same general purpose as the coil L of the anode circuit, and a resistance R to give the control electrodes a negative bias. As in Figs. 1a and 2 the coils L and L, may or may not be coupled. If they are coupled, the resistance R serves the additional purpose of preventing single-phase oscillation in which the coil Land the inherent capacities constitute the resonant circuit. As an alternative, as in Figs. 1a and 2', coil L may be omitted, with only a slight effect on the operation, resistance R then serving the purpose of absorbing the voltage differences.

At the bottom of Fig. 3b are shown the wave forms of the constant direct current i and the sinusoidal voltage 6. of one phase. The wave forms of valve or anode current 2', valve voltage or anode potential e and the control electrode potential 6 are shown in the upper part of Fig. 3b and are generally similar to those of Fig. 1a, but the current flows for one-third of a cycle instead of onehalf, and the voltages consist of sinusoidal arcs for the other two-thirds of a cycle. The middle curves of Fig. 36 show the wave forms of the current i, absorbed in one condenser and the voltage 6 absorbed in the impedance coil L.

Fig. 4a is the same as Fig. 2 except in form: in place of six separate valve structures a single structure is shown; in place of three separate generators a single directcurrent circuit D. C. is shown; and the condensers are connected in the alternatingcurrent line circuit instead of in the local valve circuit, this change being optional. Fig. 4a, however, is intended to be broader than Fig. 2 in that the valve control may be of any desired character, such as electrostatic (with the interposition of control electrodes), magnetic, mechanical,- or automatic (as in arc oscillators and rectifiers); and further, the valve converter may be either an oscillator, converting direct-current power into alternating-current power, or a rec tifier, converting alternating-current power into direct-current power.

The wave forms of the direct current i 7 dance coil L is required to a sorb and the three sinusoidal voltages e;., of the alternating current circuit are shown 111 F1g. 7, which to different scales applies to Figs. 4a, 5a and 6a. The wave forms of all valve currents are shown in the upper part of F1g. 4b; and the waves of all valve voltages are shown in the middle of this figure. These wave forms are the same as those of Fig. 1b

but are idealized, the valves being taken to in either direction. The two impedance coils L and L are not coupled.

The wave forms of currents and voltages of Fig. 5a are shown in Fig. 5b. These are the same as those of Fig.3?) idealized, except for their greater number and for the condenser current 71., which contains no even harmonies, these being canceled out in the two primary coils of each transformer.

Fig. 6a has the same valve structure as Figs. 4a and 5a and serves the same purpose.

However, in place of three and two impedance coils, respectively, it has only a single impedance coil L. This arrangement causes each valve current to flow for onesixth of a cycle, as represented at the top of Fig. 6b. The valve voltages are then zero for this sixth of a cycle, as represented in the middle of Fig. 6?). At the bottom of this figure is shown the wave form of one condenser current 2}, which is the difference between the sinusoidal alternating current between the two upper lines and the current of transformer coil 11, which balances the two rectangular currents of coils 31 and 34. At the bottom of this figure is also shown the wave form of the impedance coil voltage e which is the difference between the constant direct voltage and the six rectified sinusoidal voltages impressed successively from the transformer coils 31 to 36.

r The waves z' of Figs. 4b, 5b and 66 contain only harmonics of orders greater or less by one than a multiple of six,that is, harmonics of orders 5, 7, 11, 13, etc. In Figs. 4b and 56, those harmonics that are not common to the different waves 6 are canceled out with respect to the direct-current circuit by the connection of the different Us to a common point; so the only harmonics that may reach the external circuit are the same as in the wave 6 of Fig. 6b and are of orders which are a multiple of six. These results are in accordance with the general theory pf the cancellation of harmonics, as given ater.

All waves of Figs. 4b, 5b and'6b are for unity power-factor, as ordinarily occurs in self-controlled oscillators and rectifiers. If the power-factor is not unity, the waves'of valve voltage and of impedance-coil voltage will consist of other arcs of sinusoids than those shown.

Figs. 8 to 16-show circuits whose valves operate. at the same intervals and for the same durations as those of Figs. 4a, 5a and 6a, in accordance with the couplings of the coils L to L.,. In Figs. 8, 9, 10, 11 and 14' these coils may be coupled in any of three Ways: forming one group of six as indicatediffliig 8, which is equivalent to inserting a single impedance coil in the D. C. line circuit and which therefore causes the operation to be like that of Fig. 6a; forming two groups of three coils each as indicated 1n Fig. 11, which has an equivalent effect on operation to the two coils L and L of Fig. 0a; or forming three groups of two coils each as indicated in Fig. 14, which has an equivalent efi'ect on operation to the three coils L, L and L of Fig. 4a. Some form of coupling between these impedance coils, however, is essential. 'lhese five figures show essentially how valves can be connected in various ways with respect to the direct-current circuit; this connection being independent of the grouping of the impedance coils L to L In Fig. 8 all valves are in parallel with respect to the direct-current circuit, as was the case in Figs. 1a, 3a, 4a, 5a, and 6a. In Fig. 9 each valve is connected to a separate direct-current circuit; in this case the sum of six, three, or two valve currents (according to the mode of coupling the impedance coils) is constant, but as the individual valve currents are not constant, condensers are required across each directcurrent circuit to. absorb current variations. If the six direct-current circuits of Fig. 9 are connected in series, to form a single directcurrent circuit, Fig. 10 is obtained; if the direct-current circuits of Fig. 9 are connected two in series and three sets in parallel, Fig. 11 is obtained; while if the direct-current circuits of Fig. 9 are connected three in series and two sets in parallel, Fig. 14 is obtained.

Fig. 12 shows three valves in parallel, two groups in series, with respect to the directcurrent circuit. With the impedance coils coupled as shown they may be replaced b single impedance coil L, as shown in Fig. 13.

Fig. 15 shows two valves in parallel, three groups in series, with respect to the directcurrent circuit. With the impedance coils coupled as shown, they may be replaced by a 

